1. Field of the Invention
The present invention relates to a flexbeam and, more particularly, a flexbeam having a bearingless hub structure of a helicopter.
2. Description of the Related Art
The blades of the helicopter are coupled to the rotor shaft via the hub so as to make respective motions of flapping, feathering, and lead lag possible. As the hub structure for causing the blades to execute such three motions, there may be listed the structure using the hinges constructed by the rolling bearing, the elastomer, or the like, the structure utilizing the elastic deformation of the joint portions of the blades whose rigidity is intentionally weakened, etc.
The hub structure of the latter, which utilizes the elastic deformation in all three motions of the blade, is normally called the xe2x80x9cbearingless hub structurexe2x80x9d and comprises the flexbeam having the flapping part having flexibility, and the feathering and lead-lag part. Three motions of the blade can be attained by the deflection of the flexbeam. If such bearingless hub structure is employed, normally the controllability and the maneuverability can be improved since the hub moment is transmitted easily to the fuselage side.
As an example of the flexbeam structure in the prior art (referred to as the xe2x80x9cconventional structure (1)xe2x80x9d hereinafter), as set forth in Japanese Patent No. 2583259, there is proposed the structure in which the flapping part is constructed by jointing integrally the center member, which is made of woven-fabric composite material and is arranged in the center portion in the chordwise direction, and frame members, which is made of composite member whose fibers are oriented in one direction (referred to as the xe2x80x9cunidirectional memberxe2x80x9d hereinafter) and are arranged at the leading edge side and the trailing edge side of the center member. In this structure, the jointed surfaces between the center member and the frame members are almost normal planes that extends in the spanwise direction.
Also, as an example of another flexbeam structure (referred to as the xe2x80x9cconventional structure (2)xe2x80x9d hereinafter), as set forth in Patent Application Laid-Open No. Toku-Kai-Hei 10-287297, there is proposed the structure in which the flapping part is constructed by the center member, which is arranged in the center of thickness, upper and lower members, which are arranged on the upper surface side and the lower surface side, and the unidirectional members, which are arranged between the center member and the upper and lower members.
In the conventional structure (1), the load transmitted to the flapping part of the flexbeam is transmitted to the center member via the frame members. In this case, since the jointed surfaces between the center member and the frame members are almost perpendicular to each other, the stress and the moment are not smoothly transmitted in some cases and thus excessive shear stress and strain are caused in the inside of the frame members. Since the frame members are formed of the unidirectional member, their shear strength is low. For this reason, the shear stress caused in the inside of the frame members must be reduced.
Also, in the conventional structure (1), if the above-mentioned load is applied, a strain distribution becomes discontinuous at the jointed surfaces between the center member and the frame members and thus the large shear stress is generated in neighborhood of the jointed surfaces. Such shear stress generated in neighborhood of the jointed surfaces must also be reduced.
While, in the conventional structure (2), the load transmitted to the flapping part of the flexbeam is transmitted to the center member and the upper and lower members via the unidirectional members. In this case, the jointed surfaces between the unidirectional members and the upper and lower members are arranged near the center in the beam-thickness direction, room for improvement in the reduction of the shear stress generated in neighborhood of the jointed surfaces is still left.
A subject of the present invention is to improve structural strength of a flexbeam remarkably.
In order to overcome the above subject, as shown in FIG. 1 to FIG. 3, for example, the present invention set forth in a first aspect provided a flexbeam having a flapping part whose cross section in a direction perpendicular to a spanwise direction is formed as a rectangle, and a feathering and lead-lag part whose cross section in the direction perpendicular to the spanwise direction is formed as two substantially Y-shaped cross sections that are coupled symmetrically via a flat part, comprising: a first composite member having a plurality of first layers, which extend in the spanwise direction so as to have a plurality of fiber orientations and are laminated in a vertical direction and arranged in a center portion in a chordwise direction, and a plurality of second layers, which extend from a leading edge to a trailing edge of a beam so as to put the first composite member therebetween; and a second composite member having a plurality of loop members, which extend in the spanwise direction so as to have the fiber orientations in a same direction as an extending direction; wherein the flapping part is constructed such that the first layers of the first composite member and the second composite members arranged on the leading edge side and the trailing edge side of the beam, are jointed integrally and also the second composite members are separated by the second layers of the first composite member in a vertical direction and are jointed to the second layers, and the feathering and lead-lag part is constructed by jointing integrally the second layers of the first composite member arranged in a center of thickness, and the second composite members arranged on upper and lower surfaces of the second layers.
According to the present invention set forth in the first aspect, the flapping part is constructed by jointing integrally the first layers of the first composite members, which are laminated in plural in the vertical direction and arranged in the center portion in the chordwise direction, and the second composite members, which are arranged on the leading edge side and the trailing edge side of the beam, and also the second composite members are separated vertically by the second layers of the first composite members. Hence, a contact area between the first composite members and the second composite members can be increased in the flapping part rather than the conventional structure.
Therefore, the load applied to the feathering and lead-lag part can be transmitted effectively to the first composite members arranged in the flapping part via the second composite members. As a result, the shear stress generated in the second composite members and the shear stress generated in the neighborhood of the jointed surfaces between the first composite members and the second composite members can be reduced.
In the present invention set forth in a second aspect, in the flexbeam according to the first aspect, as shown in FIG. 2, for example, the flapping part has the first composite members for covering upper and lower surfaces of the beam.
According to the present invention set forth in the second asepct, in addition to advantages of the present invention according to the first aspect, the flapping part has the first composite members that cover the upper and lower surfaces of the beam in full width. Therefore, the jointed surfaces between the first composite members, which are arranged in the center portion in the chordwise direction, and the second composite members, which are arranged on the leading edge side and the trailing edge side of the first composite members, can be prevented from being exposed from the upper and lower surfaces of the beam. As a result, generation of cracks in the beam and spread of the cracks can be prevented.
In the present invention set forth in a third asepct, in the flexbeam according to the first or second aspect, as shown in FIG. 2 and FIG. 3, for example, the first composite member disappears from the flapping part to the feathering and lead-lag part so as to leave a portion that separates the second composite member in the vertical direction.
According to the present invention set forth in the third aspect, in addition to advantages of the present invention according to the first or second aspect, the first composite member disappears gradually from the flapping part to the feathering and lead-lag part to leave partially the portion that separates the second composite members in the vertical direction. Therefore, the first composite member that scarcely bears the load can be omitted as much as possible in the feathering and lead-lag part. As a result, the weight of the product and the material cost and the processing cost in manufacture can be reduced.
In the present invention set forth in a fourth aspect, in the flexbeam according to the first, second or third aspect, as shown in FIG. 2 and FIG. 3, for example, the second composite member is separated in the chordwise direction at the flapping part and is separated at the bent portion of Y-shaped cross section of the feathering and lead-lag part, and the portions separated at the flapping part and portions separated at the feathering and lead-lag part are continued in the spanwise direction respectively.
According to the present invention set forth in the fourth aspect, in addition to advantages-of the present invention according to the first, second or third aspect, the second composite members are separated in the flapping part in the back-and-forth direction and are separated at the almost Y-shaped folded portion in the feathering and lead-lag part, and also the portions separated at the flapping part and the portions separated at the feathering and lead-lag part are continued in the spanwise direction respectively. Therefore, the second composite members can be arranged regularly over the entire beam. As a result, high quality product with large strength can be obtained.